1. Field of the Invention
The present invention relates to a locking device, and more particularly to locking device for securing an inner tube in an outer tube of a telescopic tube assembly.
2. Description of Related Art
With reference to FIG. 6, a conventional locking device (30) for a telescopic tube assembly having an outer tube (40) and an inner tube (41) slidably received in the outer tube (40) includes a knob (31) rotatably mounted on a side of the locking device (30).
When the relative position of the inner tube (41) is to be readjusted in relation to the outer tube (40), the operator has to hold the inner tube (41) to prevent the inner tube (41) from slipping too far into the outer tube (40). Then the operator is able to unscrew the knob (51) and change the relative position of the inner tube (41) to the outer tube (40). However, when a distal end of the inner tube (41) is provided with a heavy load, e.g., an illuminating device, it is impossible for the operator to hold the weight of the illuminating device. Therefore, assistance from the others becomes essential. That is, it is almost impossible for a lone operator to finish the adjustment of the telescopic tube assembly especially when a weighty object is mounted on the top of the telescopic tube assembly.
With reference to FIG. 7, a second conventional locking device for a telescopic tube assembly having an outer tube (50) and an inner tube (51) slidably received in the outer tube (50) includes a sleeve (60) screwingly connected to the outer tube (50), a stopping sleeve (61) formed on a distal end of the inner tube (51) and a C clip (62) provided between the outer tube (50) and the inner tube (51).
When this conventional locking device is in application, the stopping sleeve (61) engages with an inner face of the outer tube (50) to stop relative movement between the inner tube and the outer tube (50,51). Furthermore, the deformation of the C clip (62) by the rotation of the sleeve (60) enhances the immovability of the inner tube (51) relative to the outer tube (50). Therefore, unscrewing the sleeve (60) enables the operator to adjust the relative position of the inner tube (51) to the outer tube (50).
With reference to FIG. 8, another conventional locking device for a telescopic tube assembly having an outer tube (70) and an inner tube (71) slidably received in the outer tube (70) includes an engaging sleeve (72) for preventing the inner tube (71) separating from the outer tube (70), multiple resilient straps (73) mounted on the outer periphery of the inner tube (71) to engage with the inner periphery of the outer tube (70), a spring (74) mounted on the bottom of the inner tube (71) and a muffler (75) received in the outer tube (70) to diminish the noise from the engagement between the resilient straps (73) and the inner periphery of the outer tube (70).
Despite the different structure of the three conventional locking devices, there is a common drawback that hinders the performance of the locking devices. That is, the friction force to prevent the inner tube from falling into the outer tube becomes weaker and weaker each time the relative position between the inner tube and the outer tube is adjusted.
To overcome the shortcomings, the present invention tends to provide an improved locking device to mitigate the aforementioned problems.